1. Field of the Invention
The present invention relates to a voltage controlled oscillator, a voltage controlled oscillator device, and a radar device provided therewith.
2. Description of the Related Art
Generally, in radar devices including an on board radar, it is important to detect whether or not the devices are operating normally to ensure their reliability.
Conventional radar devices have been disclosed in (1) Japanese Unexamined Patent Application Publication No. 5-341032, (2) Japanese Unexamined Patent Application Publication No. 6-59023, and (3) Japanese Unexamined Patent Application Publication No. 6-88870.
However, the above-described conventional radar devices have the following problems.
The radar device in (1) detects the drain voltage of a multiplier which multiplies the high frequency signal outputted from an oscillator and detects any failure from the detected value; however, it detects only the presence or absence of oscillations and it cannot detect whether or not the radar device is modulating normally. Further, this radar device cannot be applied to a configuration in which the oscillation is achieved by a direct wave without using any multiplier.
The radar device in (2) detects a failure by a change in the current of the whole circuit, and thus, it detects only the failure of an element with the current flowing therein, and it cannot detect any non-oscillating state caused by other failures. Further, it is very difficult to establish a standard for judging failures.
Since the radar device in (3) detects failure by the presence or absence of the gate current in transistors constituting oscillators and multipliers, it can detect only failure of semiconductor devices having gate terminals, and it cannot detect any non-oscillating state caused by other failures.
Accordingly, it is an object of the present invention to provide a voltage controlled oscillator, a voltage controlled oscillator device, and a radar device provided therewith which can solve the above-described problems, detect when the oscillation frequency becomes uncontrollable, detect any failure of an element with little current flowing therein, and detect a non-oscillating state even in a circuit using semiconductor elements having no gate terminals.
A voltage controlled oscillator in accordance with the present invention comprises a line, a variable reactance element connected to the line, directly or indirectly via a resonator, an oscillation device connected to the line, and a unit to output a signal detected by the variable reactance element. This means that the detection signal appears in the above-described variable reactance element when the variable reactance element is operating normally and the oscillation device is in the oscillating state, and it can be detected whether the variable reactance element is operating normally or abnormally in the oscillating state by monitoring the detection signal.
Further, the voltage controlled oscillator in accordance with the present invention may further comprise a signal output unit to detect the current flowing in the oscillation device. It can be detected whether or not the non-oscillating state is attributable to a failure of the oscillation device, and also the failure of the oscillation device can be detected. In addition, each state of failure of the variable reactance element and the oscillation device can be detected through the combination of the monitoring of the detection signal by the variable reactance element with the monitoring of the current flowing in the oscillation device.
The voltage controlled oscillator in accordance with the present invention may comprise a pick-up which is weakly coupled to the line having the above oscillation device connected thereto, and a diode for detecting a signal detected by the pick-up. This detection signal can be used even during actual operation of the voltage controlled oscillator, and the voltage controlled oscillator can be constantly monitored.
A voltage controlled oscillator device in accordance with the present invention comprises the above voltage controlled oscillator an A/D converter for converting the signal outputted by the signal output unit into digital data, and a control circuit for controlling the voltage controlled oscillator by inputting the output data of the A/D converter to control the voltage controlled oscillator, and can monitor the condition of the oscillator, and a whole voltage controlled oscillator device having the voltage controlled oscillator is appropriately operated according to whether the voltage controlled oscillator is operating normally or abnormally.
A radar device of the present invention comprises the above-described voltage controlled oscillator and a transceiver for receiving a reflected signal from a target. The target can be searched thereby in a normal condition of the voltage controlled oscillator.